Replacing Concrete Blocks with Screw Anchors – Van Diemen Aquaculture

VDA Testimonial – March 2015

Van Diemen Aquaculture operates an aquaculture farm at Rowella which is situated on a section of the Tamar river known as Long Reach. The location of the lease, covering approx 10 hectares, is in an area where strong tidal influence makes the mooring of marine infrastructure a challenge, with typical tidal flows to 2.3 knots with flood events to 3.5 knots.

In July 2010 an outgoing tide combined with a strong flood event caused the mooring system to fail; considerable damage to the farm resulted in a major rebuild of the farm’s infrastructure.

After consultation with a marine engineer decision was made to replace the traditional concrete block, plough anchor system with screw-type anchors. By early 2014 the groundwork was completed and MoorTech were engaged to supply and install N-Viro anchors. This was carried out in April/May 2014, with all anchor locations being successfully installed, even into a difficult reef section to the south of the farm.

We have found MoorTech staff helpful with advice and assistance with any challenges that have arisen. Additionally we used their versatile vessel to retrieve our old mooring system once the new anchors had been installed.

Almost 12 months on we have found the N.Viro anchors to be holding very well and they continue to live up to our expectations of them.

Up-date: June 2016

During June 2016, the Tamar River experienced record flows due to heavy rainfall in the catchment areas of the main tributaries, the North & South Esk Rivers.  This resulted in the North Esk experiencing an almost 1 in 450 year flow and the South Esk peaked at approx 1 in 100 year flow.

The combined flows resulted in the Tamar experiencing approx 1 in 200 year flows, with the maximum peak flow at the VDA site predicted in excess of 10 knots.

Due to the severity of the flood, a pre-cast concrete  Marker Pile adjacent to the farm (shipping marker for nearby Port) was washed away, while the VDA farm suffered no damage whatsoever, with all mooring lines and anchors remaining in place during this extreme weather event, which was approx double the flow of the storm which swept the farm away in 2011. This flood caused considerable damage to marine infrastructure, particularly in the north of the state.

Details: the farm lease area covers approx 10 hectares, while the farm itself comprises of 28 no. steel pens covering approx 2500 square metres.

The pens are held in place by 26 screw anchors, 9 on the sthn side, 10 on the outer (eastern) side and 8 on the northern (upstream) side. The site Geotech on this project was very variable and interesting – on the southern side  towards the reef, rock was encountered, on the eastern (river) side a sandy seabed, while on the northern side thick black mud with a high clay content

Posted in Case Studies and Testimonials.